Engine swap?

I have a 97 Burb 4x4 K2500 454 auto and average 8mpg ordinary driving and just about 10mpg on a run and often that is with just 1 person in the car, however with the full family of 6, plus gear it doesn't appear to be much different. I usually cruise at about 75mph on the open road and I do realise I am a bit heavy on the right foot around town but recently I have tried not to be to see if I can increase the economy but again it doesn't appear to have helped any if at all.
With petrol at the equivalent to $8 a gallon over here it's no joke. I have converted it to LPG which is cheaper and helps but it's still not great, so my question is this - what problems would I have in swapping the 454 for a 350, physically and mechanically I don't see much issue but what about fuel mapping (ecu's etc.) wiring, etc.
Would it work better to have a pre vortec engine with carb or stick to a fuel injected unit.
I had thought about swapping my 79 vette's 350 into it and the 454 into the vette but that was only as 350 vortec engines are not that easy to get over here.
I'm assuming that the 350 motor Burbs do get a fair bit more miles per gallon than I am at the moment.
Any thoughts or ideas to make my mind up one way or another would be appreciated, even if it's "don't bother because" etc.

It does depend. Your 454 actually gets better mileage than my 350 (about 5-6mpg in town). It depends on the condition of the engine

I think I would be crying if I went to all the trouble of swapping and ended up getting worse mileage with a smaller engine. I'm going to have to look into it more before making my mind up. The 454 has only done 90000 miles and runs well, the Vette engine is mileage unknown but also runs well and in the vette gives 15mpg on a run at around 90mph.

MY 96 454 gets about the same as my buddy's 350 tahoe.


Brian

Brian,
Does this mean that your 454 is good or your friends 350 is really really bad. (only kidding).
It would appear that some people with 350's get very good mileage and others very poor mileage, the 454's appear to be nearly all the same.
Is suppose one other idea could be to change the rear axle gearing?
I'll post another thread to see if that would help. Thanks for your imput so far.

In my opinion the 454 does not have to work as hard to move the weight. Both in excellent condition you would be suprised how little difference there is between the two.


Brian

I swapped an engine in my 87. it is a 350 with a throttle body. My old engine got in the upper teens. my new engine on a trip this weekend, all highway and interstate, it got 12 miles per gallon. I was averaging 70 to 80 all the way, 2 people in the vehicle. So my conclusion is don't check your gas mileage and keep the foot to the floor. My wife's 2000 with the 5.3 gets about 16 to 18. I bet if we ran them at 65 to 70 we would see some improvement. good luck.

I'm starting to think that I should just add fuel and as when it is needed and forget the amount of miles it does as you suggest. I would hate to think what the overall mileage would be if I left my right foot on the floor all the time, plus even though I have upped the brakes I got a bit worried when doing 100mph on one of our motorways and had to slow down a bit quick, before that incident I had thought about taking off the limiter to get a better top end but decided against it. Also it would mean I would certainly get less mpg if I had.
Anyway thanks for all your thoughts, but I am now just going to leave things alone and wait till I really can't afford to run the truck and then sell it on.

I'm starting to think that I should just add fuel and as when it is needed and forget the amount of miles it does as you suggest.
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This is the correct plan. You won't get any better mileage but you won't care. If you want great mileage get a mini-car.

I have an '88 'burb with the 350, and 400k plus miles on it. Since new, it gets the same mileage, 12.5 mpg. I would reccomend keeping the 454, if it is in good shape, you will see little difference in mileage. If it is your every day driver, i understand the pain in the wallet, but the horse power is always nice to have.

Check out www.fueleconomy.gov to get an idea of what the mpg was for each and try to get your current engine up to that performance mark.